Preheat the oven to 350F degrees and line a muffin tin with muffin papers.
In a medium bowl whisk together the flour, baking powder and salt.
Beat together the butter, sugar, and lemon zest in a large bowl until fluffy.
Mix in the eggs and vanilla extract.
In a liquid measuring cup or small bowl gently whisk together the milk and sour cream with a fork.
Beat about 1/2 of the flour mixture into the butter mixture, followed by about 1/2 of the milk and sour cream. Repeat with the rest of the flour & sour cream mixture.
Turn off the mixer and gently fold in the lemon juice.
Spoon the batter into the prepared muffin pan filling each about 2/3 to 3/4 full.
Bake in the preheated oven for 16-18 minutes or until an inserted toothpick comes out clean.
Puree the raspberries in a blender or food processor.
Push the puree through a sieve to remove the seeds. (I use a rubber spatula for this).
Add the puree without seeds to a medium saucepan over low-medium heat and bring to a boil while stirring.
Boil for 10-15 minutes or until the mixture is about 1/4 to 1/3 of the original volume and thick like jam.
Remove from the heat and place in the freezer or fridge to cool fully.
In a large bowl beat the butter until fluffy then mix in 2 cups powdered sugar.
Mix in 2-3 tablespoons of the cold raspberry sauce. (It must be cold, otherwise the frosting can separate).
Mix in the rest of the powdered sugar about 1/2 cup at a time, adding in the cream if it seems too thick.
Frost the cupcakes with a piping bag and tip (I used a 1M tip) or a knife.
* You'll need 2 medium-large sized lemons total.
**Store cupcakes in an airtight container at room temperature for up to 3 days.
***Unfrosted cupcakes can be frozen and thawed in the fridge overnight.